Field of the Invention
The present invention generally relates to a semiconductor structure. More particularly, the present invention relates to light emitting diode structure.
Description of Related Art
A light emitting diode (LED) has the characteristics of high efficiency, long lifespan, etc. and thus the LED light source has been widely applied. The light-emitting diode (LED) formed by semiconductor material of the compound of the group III-V elements is a wide band-gap luminous component, which emits the light covering all wavebands of visible light. In recent years, following the progress towards high-chroma and extreme-brightness, LEDs have gained broader applications fields, such as mega-size outdoor display boards and traffic lights, and would even substitute tungsten lamps and mercury lights to become a future lighting source with energy-saving and environmentally friendly advantages.
In a conventional GaN based LED grown on the first substrate, such as sapphire, having an insulating property, since the positive and the negative electrodes of the LED are deposited on, in general, the same side of a first surface, and the positive electrode will screen out the emitted light from the active layer of the LED. Therefore, the packaging for a GaN based LED preferably uses the flip-chip bonding method. Thus, the emitted light will pass through a second surface. Moreover, a metal reflecting layer is formed on the top-most surface of the LED in order to emit most of the emitted light towards the second surface of the LED.
However, the reflectivity of the metal reflecting layer is limited. Meanwhile, attempts to apply a distributed Bragg reflector (DBR) layer to the top-most surface of the LED have been made, wherein the DBR layer is a multi-layer dielectric having alternate layers of dielectric material with a high reflectivity compared to reflectivity of the metal reflecting layer. However, the DBR layer is made of non-conductive material, so the disposition of the DBR layer would have negative impact on electrical performance of the LED. Therefore, there is still a limit in improving the light extraction efficiency in LED packages.